Question

An electric bulb was filled with 100 cc of argon gas

(at. mass 40) at 25°C and 1 atm pressure. The

number of atoms of argon present in the bulb is

(2) 2.5 x 1021

(1) 3.3 x 1024

(3) 1.5 x 24
(4) 6.02 x 1021

Answer 1

V=100cm^3 
T=25C 
P=1atm 
R=8.21*10^-2L.atm/mol.K (universal gas constant) 
Ideal gas eqn 
PV=nRT(n stands for no.of moles) 
1*100=n*8.21*298 (K=C+273) 
n=100/(298*8.21*10^-2) 
=100/24.46 
=4.88 
No.of moles =No.of atoms/ Avogadro.n 
No.of atoms=4.88*6.023*10^23 
=2.46*10^24

Answer 2

The number of atoms of Argon present in the bulb is 2.5 × 10²¹. so option (2) 2.5 × 10²¹ , is correct.

An electric bulb was filled with 100 cc of argon at 25°C and 1 atm pressure.

We have to find the number of atoms of argon present in the bulb.

Using gas equation, PV = nRT

⇒n = PV/RT

Here,

• Pressure = P = 1 atm
• Volume = V = 100 cc = 0.1 L [∵ 1000 cc = 1 L ]
• Temperature, T = 25°C = 25 + 273 = 298K

⇒n = (1 × 0.1)/(0.082 × 298)

⇒n ≈ 0.0041

∵ number of atoms of argon = no of moles of argon × Avogadro's number.

= 0.0041 × 6.023 × 10²³

= 2.46943 × 10²¹ ≈ 2.5 × 10²¹

Therefore the number of atoms of Argon present in the bulb is 2.5 × 10²¹.